江汉盆地长湖南东部第四纪沉积物粒度与磁化率特征及其环境意义

Characteristics of grain size and magnetic susceptibility of Quaternary sedimentsin southeastern Changhu Lake,Jianghan Basin,and their environmental significance

通过对江汉盆地长湖南东部ZK06钻孔的粒度和磁化率特征分析,探讨第四纪以来研究区沉积物粒度和质量磁化率特征、水动力条件及古气候环境演化过程。研究表明,长湖南东部地区第四纪环境可划分为5个演化阶段,即阶段Ⅰ(早更新世,深度34.9~51.15 m),以河流沉积环境为主,伴有河间洼地沉积环境,质量磁化率值偏低且稳定,气候温和湿润,对应第四冰期后的间冰期;阶段Ⅱ(中更新世,深度18.9~34.9 m),湖泊沉积环境,生物丰富,质量磁化率值较低,偶有较大波动,气候总体较为温和湿润,对应第三冰期后的间冰期;阶段Ⅲ(晚更新世,深度14.4~18.9 m),河间洼地沉积环境,质量磁化率值总体稳定偏低,水动力条件弱,气候由温和湿润迅速转为寒冷干旱,对应末次间冰期与末次冰期;阶段Ⅳ(全新世早期,深度5.45~14.4 m),湖沼沉积环境,质量磁化率稳定仍保持在较低水平,水动力条件增强,说明此阶段气候开始由冷转暖,进入冰后期;阶段Ⅴ(全新世晚期,深度0~5.45 m),湖沼沉积环境,质量磁化率值显著升高,水动力条件弱,气候温暖湿润,对应冰后期。该成果为江汉盆地古气候演化研究提供了新的依据。

Based on the analysis of grain size and magnetic susceptibility of ZK06 borehole in eastern Hunan,Jianghan Basin,the characteristics of grain size and mass magnetic susceptibility,hydrodynamic conditions and paleoclimate evolution process of sediments in the study area since Quaternary were discussed.The study shows that the Quaternary environment in eastern Hunan can be divided into five evolution stages:Stage Ⅰ(Early Pleistocene,depth of 34.9 to 51.15 m)was dominated by fluvial deposits,accompanied by inter-river depression sedimentary environment.The mass susceptibility value was low and stable,and the climate was mild and humid,corresponding to the interglacial period after the fourth glacial period.Stage Ⅱ(Pleistocene,depth of 18.9 to 34.9 m),lake environment deposition,biological richness,low mass susceptibility value,occasional large fluctuations,the climate was generally mild and humid,corresponding to the interglacial period after the third glacial period.Stage Ⅲ(Late Pleistocene,depth of 14.4 to 18.9 m),the inter-river depression environment was deposited,the mass susceptibility value was generally stable and low,the hydrodynamic conditions were weak,and the climate changed from mild and humid to cold and dry,corresponding to the last interglacial period and the last glacial period.Stage Ⅳ(Early Holocene,depth of 5.45 to 14.4 m),lacustrine sedimentary environment,stable mass magnetic susceptibility remained at a low level,and hydrodynamic conditions were enhanced,indicating that the climate began to change from cold to warm and entered the post-glacial period.Stage Ⅴ(Late Holocene,depth of 0 to 5.45 m),the lake and marsh sedimentary environment,the mass magnetic susceptibility value increased significantly,the hydrodynamic conditions were weak,the climate was warm and humid,corresponding to the postglacial period.The results provide a new basis for the study of paleoclimate evolution in Jianghan Basin.